In a facsimile (fax) reproduction system, the time to scan one line is 2 ms. If the blanking interval occupies 4% of this time, what is the effective visible trace time?

Introduction / Context:
Facsimile (fax) transmission systems scan each line of an image within a given time slot. Part of this period is used for blanking or retrace, during which no visible trace is recorded. The visible trace time determines how long actual image information is being transmitted and displayed.

Given Data / Assumptions:

• Total line scan time = 2 ms.
• Blanking interval = 4% of total time.

Concept / Approach:

Visible time = Total scan time − Blanking time. Blanking time = (percentage blanking) * (total time). For 4% blanking, blanking time = 0.04 * 2 ms = 0.08 ms. Hence, visible trace = 2 ms − 0.08 ms = 1.92 ms.

Step-by-Step Solution:

Verification / Alternative check:

Cross-check: If visible = 96% of 2 ms, 0.96 * 2 ms = 1.92 ms. Both approaches confirm the same answer.

Why Other Options Are Wrong:

• 2.08 ms: would imply more than the total line period, impossible.
• 50 ms: unrelated large value, not feasible.
• 0.08 ms: corresponds to the blanking time, not the visible time.
• 19.2 ms: incorrect scaling by factor of 10.

Common Pitfalls:

Mixing blanking duration with visible trace duration; misinterpreting percentage application.

Final Answer:

1.92 ms